The present invention relates to a control device for a vehicle provided with an engine, a generator and an electrical motor.
In a series hybrid drive system, the vehicle is driven only with an electrical motor and the engine only drives the generator in order to supply electrical power to the electrical motor.
However, the engine in this type of series hybrid drive system is operated to rotate in a steady state in order to generate an approximately fixed amount of electrical power for supplying the electrical motor and excess electrical power being used to charge a battery. The vehicle may encounter running conditions which vary sharply, for example, during acceleration. Since the generated amount of electrical power may be insufficient under these conditions, it is necessary to provide a large capacity battery to compensate for the shortfall. As a result, the size and weight of the battery is increased.
It has been proposed to calculate the electrical power consumed by the electrical motor for vehicle running and to control the engine and generator in order to generate a corresponding amount of electrical power by the Japanese Patent Application No. 11-172426.
When the amount of electrical power consumed by the electrical motor corresponds with the amount of electrical power generated by the generator, the battery capacity may be kept to a minimum and it is possible to downsize the battery and reduce costs.
However although a relatively accurate correspondence of the power generated by the generator and the power consumed by the motor is possible when the vehicle is running under steady-state conditions, there is often a shortfall in the generated amount of power during vehicle acceleration or the like and thus it is necessary to compensate the required amount of power with the battery.
This is as a result of the following reasons. Due to the inertial weight of the rotating components of the generator or engine, a part of the engine output is used in order to increase the rotation speed of the rotating components of the generator and the engine-itself when acceleration is required. That is to say, a part of energy is consumed in order to increase the inertial energy of the rotating components, therefore the amount of generated power is reduced to that extent.
Thus the generated amount of electrical power will be less than the power requirements of the electrical motor. This deficit in the generated amount of electrical power must be compensated for by a battery and thus the battery must have a correspondingly large capacity.
It is therefore an object of this invention to make the generated power of the generator accurately correspond to the consumed electrical power as drive output of the electrical motor even under transient running conditions such as acceleration.
It is a further object of this invention to minimize a required battery capacity.
In order to achieve above the objects this invention provides a controller for a vehicle which has an engine, a generator connected to the engine, an electrical motor connected to the vehicle drive shaft and a battery electrically connected to the generator and the electrical motor, the controller comprises sensors to detect operational conditions of the vehicle, and a microprocessor. The microprocessor is programmed to calculate a first parameter showing a target output of the electrical motor based on operational conditions of the vehicle, to calculate a second parameter showing a target output of the engine based on the first parameter, to calculate a third parameter showing a target rotation speed of the generator based on the second parameter, to calculate a fourth parameter showing a generated output of the generator based on the second parameter, to calculate a fifth parameter showing a target output of the electrical motor by limiting the first parameter in response to the fourth parameter, to control the operation of the engine based on the second parameter, to control the operation of the generator based on the third parameter, and to control the operation of the electrical motor based on the fifth parameter.
The details as well as other features and advantages of the invention are set forth in the remainder of the specification and are shown in the accompanying drawings.